Gaseous reservoir and heater for hydrogen thyratrons



N. REINHARDT June 6, 1967 GASEOUS RESERVOIR AND HEATER FOR HYDROGEN THYRATRONS Filed Jan. 28, 1966 Fig. 5.

NICHOLAS REINHARDT INVENTOR.

United States Patent 3,324,331 GASEQUS RESERVOIR AND HEATER FOR HYDRGGEN THYRATRONS Nicho as Reinhardt, Lexington, Mass, assignor to EG&G, Inc., a corporation of Massachusetts Fiied Jan. 28, 1966, Ser. No. 523,595 4 Claims. (Cl. 313180) This invention relates to gaseous discharge devices and more particularly to reservoirs for replenishing the gas in such devices.

Reservoirs have been used for a long while to replace gas that has been used up during operation of gaseous discharge devices. This use of the gas within the device is commonly referred to as clean-up and although the nature and causes of clean-up are not fully understood, reservoirs have substantially extended the life of these devices by emitting gas to replace that used up in the device. The reservoir element is loaded with gas when the device is assembled and its temperature is elevated to permit emission of the gas in response to variations of pressure and temperature within the discharge device. Although they served a very important function, prior art reservoirs were one of the major problem areas in highpower discharge devices, such as thyratrons, rectifiers and the like. The most vulnerable part of these reservoirs was the heater which was required to control the reservoir temperature. The reservoir heaters are considerably smaller and more fragile than the huskier cathode heaters in such discharge devices, and are particularly vulnerable to severe environmental shock and vibration. In many cases, it had to be clamped or restrained in an effort to provide greater stability and longer life. The problem be came much greater when the reservoir was scaled down as small as possible for use in miniaturized ceramic-metal hydrogen thyratrons and rectifiers because it became increasingly more difiicult to maintain the heater insulation out of contact with the active reservoir material. Such contact caused deleterious chemical reactions at operating conditions. It was important, however, to hold the heater as close to the active reservoir material as practical and to have it radiate its power directly thereto for the best electrical and thermodynamic operation of the reservoir. Liners and shims of a material compatible with both the heater and the reservoir material have been disposed adjacent the heater to permit clamping, sandwiching, surrounding or otherwise restraining it from excessive movement. Such measures isolate the active material from its sources of heat, interfere with heat transfer, require excessive heater temperature and result in a degradation of electrical and thermodynamic characteristics of the reservoir.

Prior art heating elements were a compromise between two sources of reservoir breakdown. If the heating element were placed in contact with the reservoir material, then the alumina coating normally used on the heating wire would react with the reservoir element, usually either titanium or zirconium, and thus cause breakdown. The alternative was to provide considerable spacing between the two. As a compromise between these alternatives, the heating element was suspended in an oven-type enclosure adjacent to or inside the active reservoir elements. In such an arrangement, the heater was weak and fragile, and readily susceptable to damage and destruction and the resulting reservoir itself was bulky and unsuited for use in miniaturized tubes.

It is, therefore, an object of this invention to provide an e ficient and rugged reservoir, not subject to the foregoing disadvantages.

Another object is to provide a means for holding the gas-loaded reservoir element and its heater in close proximity to each other without untoward chemical reaction.

In summary, this invention is a gaseous reservoir which utilizes a thin molybdneum member having a large open area therein, disposed intermediate and in contact with the reservoir element on one side and the heater element on the other.

Other objects of this invention will be pointed out in the following discussion considered with the attached drawings in which:

FIGURE 1 is a sectional view of a gaseous discharge device;

FIGURE 2 is a plan View of an important element of this invention;

FIGURE 3 is a sectional view of the preferred embodiment of this invention; and

FIGURE 4 is a sectional view of a modification of the invention.

Referring first to FIGURE 1, a gaseous discharge device in the form of a hydrogen thyratron is shown as a typical environment for the subject invention. The reservior 4, which constitutes the essence of the invention, is shown disposed beneath the cathode electrode 5. This hydrogen thyratron may be, for example, the type de-' scribed in US. Letters Patent No. 3,175,114, issued on Jan. 22, 1963, to K. J. Germeshausen, and assigned to the assignee hereof. The electrode elements include a cupshaped anode 1, an inverted cup-shaped control electrode 3 and a vane cathode 5. These three electrodes have externally extending flanges 1, 3' and 5' respectively, which pass through ceramic Wall sections 2. The control electrode 3 may be apertured at 7 and a grid baflle 9 overlying the aperature 7 may also be provided. A cathode bafiie is shown as 11. This description is provided to indicate the environment in which the applicants invention resides. A further description of this gaseous discharge device and its internal features is omitted so as not to detract from the significance of the present invention.

FIGURE 2 shows separation member 20, preferably of molybdenum, which is employed in reservoir 4 to separate the reservoir material 8 from the heating element 19 and yet maintain them in close proximity. A large number of small openings 15 are made according to a predetermined pattern on member 20. The purpose of these openings is to facilitate the radiation of heat from heating element 10 to reservoir material 8. These openings 15 may be made in any suitable manner. I have found, however, that photoetching is the most suitable means for accomplishing this end. A complete disclosure of a satisfactory photoetching technique is found in my copending application for US. Letters Patent Ser. No. 273,819, filed Apr. 18, 1963.

These openings 15 may also be obtained by using a wire mesh or grid-iron screen or by machining or stamping metal plates. Wire screens are less desirable because they have raised areas at the wire intersections which produce abrasion of the heater during the slight movement thereof caused by shock and vibration. Machining or stamping of metal plates tends to produce burrs which may also cause abrasion and the percentage of open area obtainable in this way is limited. These other methods for producing the openings 15 may be employed but they are not preferred because they introduce disadvantages which shorten tube life.

The size of the openings 15 are preferably very small, particularly if the reservoir material 8 is in granular or powder form as shown in FIG. 4. In which case, the openings 15 must be smaller than the size of the reservoir material to maintain it in position. In the case of reservoir plates as shown in FIG. 3, openings 15 must be small enough to prevent contact even with slight warping or bowing of either the heater or the reservoir plate. In any event, the percentage of open area of member 20, represented by openings 15, should be as great as possible in order to permit maximum heat transfer. The upper limit is dictated by the need to prevent any possible contact between the insulator heater and the active reservoir material. We have found for particular purposes, that the open spaces between 60 and 75 percent of the total space provide sutficient heat transfer and maintain the desired physical separation of the heater and the reservoir material. It is desired to maintain member 20 uniformly thin to effect separation of the reservoir material 8 and the heater without adding appreciably to the mass or bulk of the reservoir construction. Excessive mass results in undesirably long warm-up times. Excessive bulk cannot be tolerated in a miniaturized device. A plurality of tabs 13, preferably four as shown in FIGURE 2, are made a part of member 20 by the photoetching process. During the formation of member 20, slots 14 are produced in each tab 13. These slots provide a means for securing member 20 in position.

Referring now to FIGURE 3 a reservoir constructed in accordance with the teachings of this invention, shows a reservoir 4 constructed of stacked plates of active reservoir material 8 disposed on either side of an insulated metallic heater 10 and separated from it by the aforesaid separation members 20. Such a reservoir configuration without member 20 is disclosed in US. Letters Patent No. 3,222,561, issued Dec. 7, 1965 to the applicant herein. As pointed out above, members 20 have a large number of openings to allow the heat produced by heater 10 to radiate directly to reservoir material 8. The reservoir material 8 may be slightly cupped, or an extra ring of either reservoir or inactive material may be disposed about the periphery of heater 10 to prevent loss of heat out the side of the structure.

Although shown slightly expanded vertically in FIG- URE 3 for clarity, the entire structure 4 is clamped tightly together by wedging-type ears 18 on legs 17 passing through slots 14 of tabs 13, thus supporting and aligning the reservoir structure 4 within the body of the thyratron shown in FIGURE 1. In this preferred embodiment of this invention, member is a thin molybdenum plate, separating the alumina coated heater from the gas-loaded titanium reservoir material. At the normal reservoir operating temperatures, that is 750 C., the molybdenum of member 20 is inert to both alumina and titanium, thus eliminating any dangers of fusion, contamination or breakdown.

In FIGURE 4, a reservoir is shown constructed in accordance with a modification of this invention. Reservoir chamber 6 has a top protective cover 21, which is partially open to permit the gas to flow from the reservoir through screen 22. The reservoir material 8 is held within chamber 6 by the aforesaid separation member 20 which is maintained firmly against chamber 6 by holding pin 19 which passes through chamber extension 18, member 20 and base plate 12. A metallic heating element 10 covered with a thin insulative coating, such as alumina, is shown disposed between and in contact with member 20 and base plate 12. Base plate 12 is solid and may have an upper reflective surface to radiate heat toward reservoir material 8. As pointed out above, member 20 has a large number of openings 15 to allow the heat produced by heater 10 to radiate to reservoir material 8. A side wall may be disposed about the outer edges of the space between member 20 and base plate 12 to prevent loss of heat and to increase the heating efficiency.

It should be noted that the heating element 10 may be formed in a number of different configurations, for example, spiral, zig-zag, rectangular, solid, reticulated, triangular or non-geometric free-form convolutions. It is not essential, although it is preferred, that the heating element be maintained in contact with member 20.

Although I have disclosed my invention in the terms of its preferred embodiment, it will be evident to those skilled in the art of gaseous reservoirs that it has greater scope and such scope is deemed to fall within the spirit of this invention.

I claim:

1. A reservoir for a gaseous discharge device comprisa reservoir material having an absorbed quantity of the fill gas of the discharge device;

a heating element having a thin insulation coating thereon disposed in close proximity to said reservoir material; and

a member disposed intermediate the reservoir material and the heater and having a plurality of openings therein to permit heat transfer from the heater to the reservoir, said member being composed of a substance that does not react to the reservoir material or heater insulation at operating temperature.

2. A reservoir for a gaseous device comprising:

a zirconium or titantium reservoir material having an absorbed quantity of the fill gas of the discharge dev1ce;

an alumina-coated heating element disposed in close proximity to the reservoir material for raising the temperature thereof; and

a thin molybdenum member disposed intermediate the reservoir material and the heater and having a plurality of openings therein to permit heat transfer from the heater to the reservoir material.

3. A reservoir as claimed in claim 2 in which said member is in contact with the reservoir material and the heater.

4. A reservoir as claimed in claim 2 in which the openings in said member form a greater percentage of the members area than the closed sections.

References Cited UNITED STATES PATENTS 2,572,881 10/1951 Rothstein 3l3180 2,919,368 12/1959 Goldberg et al 313 3,095,518 6/1963 Creedon et al. 313-180 JAMES W. LAWRENCE, Primary Examiner.

C, R. CAMPBELL, Assistant Examiner. 

1. A RESERVOIR FOR A GASEOUS DISCHARGE DEVICE COMPRISING: A RESERVOIR MATERIAL HAVING AN ABSORBED QUANTITY OF THE FILL GAS OF THE DISCHARGE DEVICE; A HEATING ELEMENT HAVING A THIN INSULATION COATING THEREON DISPOSED IN CLOSE PROXIMITY OT SAID RESERVOIR MATERIAL; AND A MEMBER DISPOSED INTERMEDIATE THE RESERVOIR MATERIAL AND THE HEATER AND HAVING A PLURALITY OF OPENINGS THEREIN TO PERMIT HEAT TRANSFER FROM THE HEATER TO THE RESERVOIR, SAID MEMBER BEING COMPOSED OF A SUBSTANCE THAT DOES NOT REACT TO THE RESERVOIR MATERIAL OR HEATER INSULATION AT OPERATING TEMPERATURE. 